The present invention relates to a control device for a main-light circuit of a motor vehicle the circuit is provided with (a) inputs which are connectible to one terminal of a voltage source and of which inputs one is intended to be connected via a vehicle light selector switch for selecting a desired vehicle lighting facility; (b) outputs which are intended for connection to the main lights of the vehicle and of which outputs at least one is intended for connection to the dipped-beam system and at least one is intended for connection to the main-beam system; (c) outputs which are connectible to the outer terminal of the voltage source via the vehicle chassis and of which outputs one is intended to be connected via a light dimmer switch intended for switching between dipped beam and main beam; adn also with (d) beam changing relays connected to such inputs and outputs, relays being connected to an electronic control unit which activates the relays as a function of whether the input which is connectible to the lights switch and the output which is connectible to the dimmer switch are connected to the voltage source or not.
Present day control devices of the above-described kind are comprised entirely of relays and are not sufficiently reliable. The relays included are often relatively complicated and therefore difficult to manufacture. Good functional reliability, however, requires high manufacturing precision. Another drawback with present day control devices is that a relay malfunction will jeopardize the possibility of switching on the vehicle main lights. Another drawback with present day control devices is that when switching on the vehicle main lights the main beam is often switched on without always being noticed by the driver. This is an unfortunate occurrence from the aspect of traffic safety.
An object of this invention is to provide an improved control device which does not have the foregoing drawbacks and which is simpler to manufacture and is more reliable in operation.
This object is achieved in accordance with the invention in that the so-called rest contact of a first monostable relay is connected to the control device input intended for connection to the light selector switch, and in that the input of such relay is connected to the input of a second monostable relay whose rest contact is connected to the dipped beam output. Accordingly when no relays can be activated there is provided a current path for supplying current to the dipped beam facility. In this way there is obtained for the supply of power to the dipped beam an emergency current path which can be supplied through the light selector switch. This embodiment enables dipped lights to be used even when the control device malfunctions, which is highly advantageous from the aspect of traffic safety.